Lithographic processes generally employ at least two steps to prepare a plate for use in a printing press, namely exposure of a plate coated with a photosensitive composition to a positive or negative information-bearing light source to create a photoimage and a subsequent development step. Typically, development involves washing away material from the portions of the plate exposed to a light source in a positive acting system or from the unexposed portions of the plate in a negative acting system. The development is aided by a developer solution which may be highly alkaline, e.g., at a pH of 13 or greater, and which may contain organic solvent. Alternatively, heating has sometimes been employed to effect development of the photoimage.
Both of the above-described development processes tend to suffer from the drawback of being relatively time-consuming, environmentally unsound because of development liquid effluent, and sometimes expensive. Furthermore, when volatile organic or strongly alkaline developer solutions are used, their disposal presents a particularly difficult environmental problem.
The industry has long desired photosensitive compositions which can be used in development processes which do not have the above-described drawbacks.
A variety of different materials have been used in photosensitive compositions in the past. Photosensitive compositions employing polymers with pendant acid sensitive moieties have been described in the art (Ito, H.; Ueda, M. Macromolecules 1988, 21, 1475-82). o-Nitrobenzyl substituted polyacrylates have been described in U.S. Pat. No. 3,849,137 (Nov. 19, 1974; Barzynski). t-Butyl substituted polyacrylates have also been reported (Ito, H.; Willson, C. G. in Proc. SPIE-Int. Soc. Opt. Eng. 1987, 771, 24; and U.S. Pat. No. 4,491,628 (Jan. 1, 1985; Ito).
U.S. Pat. No. 4,963,463 (Koshiba et al.) claims a radiation sensitive resin composition comprising an alkali soluble resin, an o-quinone diazide, and acid sensitive esters of nitrobenzyl or cyanobenzyl alcohol.
End-capped polyphthalaldehyde has been employed in imaging systems in combination with onium salts which were used as a source of photogenerated acid (Ito, H.; Willson, C. G. Polym. Eng. Sci. 1983, 23, 1013). Photoresists based on thermal polycarbonate degradation in the presence of photogenerated acid have also been described (Frechet, J. M. J.; Bouchard, F.; Houlihan, F. M.; Kryczka, B.; Eichler, E.; Clecak, N.; Willson, C. G. J. Imag. Sci. 1986, 30, 59). Both of these systems function by cleavage of the polymer backbone.
Canadian Patent No. 672,947 (Canadian Industries Ltd.) describes protective films comprising copolymers of tetrahydropyran-2-yl acrylates, and glycidyl esters of acrylates. These films are thermally processed, thereby effecting cleavage of the tetrahydropyran-2-yl groups, and subsequently causing cross-linking of the carboxylic acid and the epoxy residues.
Benzyl, benzhydryl, and triphenylmethyl acrylates have been imaged using high energy radiation (e.g., electron beam, x-ray, and ion beam) sources followed by development with aqueous alkaline solutions as described in Japanese published applications 59-075244 (Apr. 27, 1984; Hitachi, Ltd.), and 58-068743 (Apr. 23, 1983; Hitachi, Ltd.).
Dimethylbenzyl methacrylates have been employed in combination with iodonium salts as deep-UV photoresists (Ito, H. Polym. Mater. Sci. Eng. 1989, 60, 142).
.alpha.-Substituted benzyl methacrylate polymers have been photoimaged and developed with an alkaline developer (Ito, H.; Ueda, M.; Ebina, M. ACS Symp. Ser. 1984, 266, 57-73).
Japanese published applications 63-256492 (Oct. 24, 1988; Fuji Photo Film Co., Ltd.) and 63-317388 (Dec. 26, 1988; Fuji Photo Film Co., Ltd.) describe several direct-image lithographic plate formulations employing polymers having side-chain groups which, following an etching development step, cleave to form hydroxyl and carboxyl groups.
Japanese published patent applications 53-094691 (Oct. 24, 1989, Fuji Photo Film) and 53-100192 (Oct. 30, 1989, Fuji Photo Film) describe lithographic plates containing polymers with acid labile groups including some alkoxyalkyl esters. The plates also contain cross-linking agents which appear to cross-link with carboxylic acid residues as they are formed. These plates appear to act in a negative-tone and may involve a development step.
Japanese published application 62-299,313 (Jun. 1, 1989, Matsushita Electric Industrial) describes the use of polymers containing acid anhydride residues in combination with o-nitrobenzyl esters of carboxylic acids. These polymers are sensitive only to UV radiation.
U.S. Pat. Nos. 4,072,527 and 3,458,311 are representative of a class of patents which disclose the use of non-photosensitive cover layers as oxygen barriers, particularly on acryloyl (and methacryloyl) containing photosensitive printing plate forming articles. The oxygen barrier layer is water-removable and is removed during the wash development of the printing plate.
U.S. Pat. No. 5,258,263 describes a no-process printing plate (i.e., a photosensitive article which does not have to be liquid developed before being used on press). This article has two photosensitive layers on a substrate. The photohardening layers are a hydrophilic photohardening layer over-coated with a hydrophobic photohardening layer as a top coat. The top-coat layer is clearly photosensitive (in that it hardens when irradiated to alter its removability during development processing) and is removed by wash-off development in non-irradiated areas.
U.S. Pat. Nos. 5,102,771 and 5,225,316 describe photosensitive compositions which comprise: (a) a photoinitiator which generates an acid upon exposure to radiation; and (b) a polymer having acid labile groups pendant from the polymer backbone, said pendant groups being represented by the formula ##STR1## wherein:
R.sup.1 and R.sup.2 each represent H or an alkyl group with 1 to 18 carbon atoms with the proviso that at least one of R.sup.1 and R.sup.2 must be hydrogen; R.sup.3 represents an alkyl group with 1 to 18 carbon atoms; or any two of R.sup.1, R.sup.2, and R.sup.3 may together form a substituted or unsubstituted ring having from 3 to 36 carbon atoms; and T represents a divalent linking group bonded to the polymer backbone contains a total of from 0 (a covalent bond) or 1 to about 18 carbon atoms where up to one of each three carbon atoms may be replaced by oxygen, nitrogen, or sulfur atoms or combinations thereof. These compositions are used on an imageable article which comprises a substrate coated with the above-described photosensitive composition. These articles are used in processes in which the imageable article is irradiated and then directly placed on press for use as a printing plate without liquid wash-off development.